1. Field of the Invention
This invention relates to an improved method for the ion exchanging and impregnating of catalysts and catalyst supports. More particularly, this invention relates to an ebullated bed technique for the ion exchange and impregnation of catalysts.
2. Description of the Prior Art
Heterogeneous catalysts are essential processing aids in the chemical process industries because of the enormous value they add to feedstock material. They are used in a wide variety of chemical process applications. In addition to their well-known uses in the refining industry, catalysts play a wide role in chemical petrochemical operations.
Heterogeneous catalysts are produced in a variety of physical forms and sizes, ranging from the micron size used in fluidized-bed operations to particles as large as one-half inch, which may be in the form of beads, extruded pellets, tablets or granules. The size and shape of the catalyst is dictated by the process in which it will be utilized.
J. Y. Livingston, Hydrotreating Catalyst Properties Do Affect Performance, AICHE Meeting, Mar. 12, 1973, Paper 9B, classifies the manufacturing of catalysts into three general approaches:
Precipitation or Coprecipitation PA1 Impregnation (including Ion Exchange) PA1 Comixing or Compounding
A precipitated or coprecipitated catalyst is derived from a solution. An impregnated catalyst is one in which a previously formed support is coated with or dipped in a solution of another metal or metals. A comixed or compounded catalyst is one in which all the ingredients are mechanically mixed together before the catalyst is formed into its final shape.
The manufacturing steps for all three of the above approaches are similar, however, there are differences in the order in which each of the steps is conducted. Catalyst production generally involves the unit operations of dissolving, precipitation, filtration, centrifugation, drying, impregnation, calcination, ion exchange and crystallization.
A great number of solid catalysts are produced by extending the desired catalytic material through the pores or over the surface of a carrier by means of impregnation. This not only secures the catalytic material, but puts it in a form readily handled, or exposes a greater surface for maximum utilization and efficiency.
The general steps in the impregnation approach include precipitation of a support followed by washing and drying, forming of the support, activation of the support, impregnation from metallic solutions, drying, washing or decomposing and final activation. Final activation of the catalyst is usually accomplished by thermal means at temperatures in the range of 600.degree. F. to 1600.degree. F. Thermal treatment in air results in a catalyst with the highest possible surface area for the material being processed.
Impregnation and ion exchange of catalysts and catalyst supports is broadly old. Typical impregnation procedures which include the dipping or soaking technique and the spraying technique are described in the following articles, all of which are incorporated herein by reference: W. D. Stillwell, Preformed Catalysts and Techniques of Tableting, INDUSTRIAL AND ENGINEERING CHEMISTRY, Vol. 49, No. 2, Feb. 1957, p. 245; G. W. Higginson, Making Catalysts--An Overview, CHEMICAL ENGINEERING, Sept. 30, 1974, p. 98; and F. Traina and N. Pernicone, Preparation Techniques and their Influence on the Properties of the Solid Catalysts LA CHIMICA E L'INDUSTRIA, Vol. 52, N.1, Gennaio 1970, p. 1.
There are two basic approaches to impregnation and ion exchange. The more obvious approach is the "dipping" or "soaking" technique in which the preformed substrate is immersed in a solution of the impregnating salt. Controlled variables are soak time, temperature and solution pH. Since the substrate usually has a given capacity to absorb solution within its pore structure, the solution concentration determines the amount of metal salt absorbed in the substrate. A drainage period follows, then drying and a salt decomposition step in arriving at the finished catalyst. The ability to control the final metal concentration in the dipping technique is less certain than in the spraying technique.
The dipping or soaking of preformed shapes is usually carried out in baskets which are dipped into the impregnating/ion exchange solution. Tough granular supports and coarse powders are usually handled by a dragline or spiral conveyor moving through a dip tank. Each dipping is usually followed by draining, drying and calcining to complete the cycle. Another technique for dipping or soaking involves pumping a solution of material to be impregnated or ion exchanged through a packed column of catalyst carrier. The concept of the present invention deals with this particular technique.
Batch process impregnation can be used for granules (beads, extruded pellets, etc.). The impregnation is achieved in a medium-sized barrel of a few cubic meters, wherein the useful volume is about one cubic meter. The unit load can range from about 500 kg to 2 tons according to the apparent density of the support. The barrel, whose inner surface is fitted with blades having an appropriate shape, can turn on its rollers in both ways--one way for filling and impregnation time (from a few minutes to one hour) and the other way for emptying (a few minutes). The impregnating solution is also prepared in batch.
The other main approach to impregnation exchange is the "spraying" technique. In this technique, the catalyst carrier is evacuated and over it is sprayed, while conveniently stirred, a volume of solution of active components not higher than the carrier's absorptive capacity. In lieu of stirring, the catalyst can be contained in a vessel which is designed to rotate during spraying. The vessel can be equipped with a heated shell to carry out catalyst drying. After spraying and drying, the catalyst is calcined.
The vessel utilized for a continuous spraying process would be smaller than the vessel used if a batch process impregnation was employed. A typical vessel size for a continuous spraying process is from about a few hundred liters to about one cubic meter. The preparation of the impregnating solution is achieved continuously by means of a metering pump. The solution flowrate is adjusted to the feedrate of the support. Continuous spraying processes allow for high production rates.
The impregnating of fine powders (alumina, silica-magnesia) is achieved in a horizontal double-screwed mixer. The fine powder is impregnated by means of a water distributor fitted with holes whose diameter is adjusted by means of diaphragms.
The spraying technique is usually preferred over the conventional soaking or dipping technique since the spraying technique usually results in a more uniformly impregnated/ion exchanged catalyst. Also in the spraying technique, there is a more accurate control of the metal concentration. When dealing with expensive metals, the cost of catalyst production can be drastically reduced by the judicious control of metals.
Heretofore conventional impregnation and ion exchange techniques sometimes resulted in non-uniform distribution of impregnation/ion exchange solution on the catalyst carrier. Also said conventional techniques have been known to unduly damage catalysts due to the various stirring and mixing operations employed. It would thus be very advantageous to have a process for uniformly impregnating and ion exchanging catalysts without undue catalyst damage.
Ion exchange of crystalline zeolites is disclosed in numerous patents such as U.S. Pat. Nos. 3,140,249; 3,140,251; 3,140,253; and 4,083,807. Such ion exchange is generally accomplished by contacting the zeolite with a solution of a salt, the cation of which it is desired to replace for the alkali metal in the crystalline zeolite. Generally speaking, multiple exchanges have been used to reduce the alkali metal content to a level wherein the residual exchangeable alkali metal is such that it does not adversely affect catalysis. Some methods have heretofore been proposed which embody a calcination step between multiple exchanges. U.S. Pat. Nos. 3,402,996 and 3,677,698 disclose such multiple ion exchange processes.
An improved process for ion exchange treatment of zeolitic FCC catalysts using moving sectionalized vacuum belt fitters operated to include flooded perculation zones and in which ion exchange treatment takes place with a countercurrently flowing ion exchange liquid is disclosed in U.S. Pat. No. 4,048,284.
Impregnation of crystalline zeolites is disclosed in numerous patents such as U.S. Pat. Nos. 3,965,208; 4,002,698 and 4,034,053. Impregnation is generally accomplished by contacting a zeolite with a solution containing the material to be impregnated. The mixture of the zeolite carrier and said solution is stirred. The solids are then filtered out, washed, dried and then calcined.
Ebullated bed technology is well described in U.S. Pat. No. 2,987,465 and the ebullated bed technique has been used in the past in various hydrogenation and hydrotreating processes and such uses are disclosed in U.S. Pat. Nos. 3,183,178; 3,183,180; 3,418,234; 3,705,850; 3,761,393; 3,948,756. The application of ebullated bed techniques to catalyst impregnation and ion exchange is novel.